Methanolysis, intramolecular

Scheme 7 Generalized mechanism for the methanolysis reaction of 32, HPNPP proceeding via intramolecular cylcization to form a 5-membered cyclic phosphate which undergoes subsequent opening via attach of methoxide.

The reactivity of the intramolecularly coordinated silenes 929, 934, and 935 has been investigated. The hydrolysis and methanolysis of 929 proceed via formation of Si-O bonds and yield the products 936 and 937 (Scheme 132). The reaction of 929 with benzaldehyde can be regarded as sila-Wittig reaction, and proceeds via the initial formation of the cycloaddition product 938, which rearranges into the cyclodisiloxane [R(Me3Si)SiO]2 939 (R = 8-dimethylamino-naphthyl-l-yl) and l,l-bis(trimethylsilyl)-2-phenylethene 940 (Scheme 132). Methyl iodide catalyzes the isomerization of 929, which proceeds via addition to the Si-C... 

Methanolysis can occur via inter- or intramolecular nucleophilic attacks by MeOH at the carbon atom of a Pd-acyl moiety and produces an ester end group and a Pd - H+ species. Again, the hydride may deprotonate with formation of less active Pd(0) and dimeric species (Fig. 3) [47,57]. 

The authors suggest a scheme for the reaction mechanism in which the initial step involves a 1,4-addition of oxygen to the substituted naphthalene nucleus (35-+131). This is followed by methanolysis and intramolecular Diels—Alder addition giving the cyclization product 130, which appears to be unstable compared to 127. 

Examples of possible intramolecular general acid-base catalysis were reported by Kupchan et al. (1962). The methanolysis of coprostanol acetate and coprostane 3/3, 5/3-diol 3-monoacetate [12] in aqueous methanol was conducted in triethylamine-triethyl-ammonium acetate buffer. The rates of methanolysis at constant... 

The chain transfer by intramolecular methanolysis is illustrated in Scheme 7.18. 

The aqueous methanolysis of 3,4-dihydro-27f-pyrano[3,2-(r]pyridinium a-D-A -acetylneuraminoate has been studied and is believed to proceed via dissociative transition states with no intramolecular nucleophilic participation by the anomeric carboxylate group <2004JP0478>. The synthesis of the starting substituted sugar is also reported. 

Many reactions have been performed in the presence of a solvent. However, the solvent must be chosen carefully to avoid reaction with polymer. For example, the low yield for grafts of acrylonitrile on polyamides in the presence of methanol has been shown to be due to the methanolysis (18,31). Generally speaking, the grafted products are principally obtained however minor amounts and homopolymers can also result. The homopolymerization proceeds by an intramolecular transfer reaction between macroradicals and monomers. The amount of homopolymer depends on the system. Details on systems already investigated will be described in the next section. 

Attempts to functionalize the homoallylic alcohol 15 quickly revealed that this product of an intramolecular aldol condensation was sensitive to base. Fortunately, heating with thiocarbonyldiimidazole effected clean dehydration to give predominantly the desired regioisomer of the diene. Methanolysis followed by oxidation then gave the triketone 1, which on epoxidation with MCPBA gave 2 as the minor component of a 3 1 mixture. 

Evidence has been provided604 for intramolecular nucleophilic catalysis by the carbonyl group during methanolysis of o- and / -formylbenzenesulfonates in basic media (see Scheme 121). A theoretical study of the zwittazido cleavage of 4-azido-2-pyrrolinones has been undertaken,605 and ab initio calculations have been carried out to examine the possibility of the existence of a hexacoordinate phosphorus intermediate (469) in the migration reaction (468) —> (470) of dimethyloxyphosphorylthreonine.606... 

The formation of methanolysis product 25 (R = Me) was easily understood in terms of ketene acetal structure 24. However, the isolated thermal product 26 is not directly derived from the ketene acetal 24. It is not unreasonable to suggest that thermal transformation of the [2 + 4] adduct 24 into the [2 + 2] adduct 23 takes place, followed by intramolecular migration of the trimethylsilyl group to afford vinylsiloxane... 

Methanolysis of 8-acetoxymethyl-5,6,7,8-tetrahydro-lH,4aH-pyrido[l,2-a] pyrimidin-l-one 78 under Zemplen condition in MeOH with catalytic amount of Na yielded 8-hydroxymethyl derivative 79, which underwent ring transformation by intramolecular attack of the hydroxy group on the carbonyl group to give oxazino[3,4-a]pyridinone 80 in 70% yield (07CAR1813). 

N. A. Hughes, Formation of methyl 2,6-anhydro-3,4-0-isopropylidene-u- and -fl-n-talopyranosides by an intramolecular displacement in the methanolysis of 1,6-anhydro-3,4-0-isopropylidene-2-0-methylsulphonyl-J6-D-galactopyranose, J. Chem. Soc. C, (1969) 2263-2266. 

The mechanism of methanolysis at 25 °C of / -nitrophenyl acetate (PNA) by a Zn2+ (MeO-) complex of 1,5,9-triazacyclododecane (79 M = Zn) involves pre-equilibrium binding of PNA to (79 M = Zn) followed by rate-limiting intramolecular attack of the coordinated methoxide to form a tetrahedral intermediate stabilized via coordination to the Zn2+.79... 

Khan and Arifin reported a study involving the kinetics and mechanism of an intramolecular general base-catalyzed methanolysis of phenyl salicylate in cationic micellar media [12]. The authors showed the participation of methanol in the reaction via its partitioning into the micellar pseudophase and thereby modifying the overall aggregate microenvironment. 

The aminolysis and methanolysis of ionized phenyl salicylate (189) have been examined under micellar conditions. The effect of CTABr on the rates of aminolysis of (189) by -butylamine, piperidine, and pyrrolidine is to bring about a rate decrease (up to 17-fold with pyrrolidine). The results are interpreted in terms of binding constants for the amines with CTABr and the pseudo-phase model.The effects of mixed surfactants SDS and CTABr on the methanolysis of (189) and the alkaline hydrolysis of phenyl benzoate suggest that micellar aggregates are involved in the processes.The effects of NaOH and KBr on the intramolecular general base-catalysed methanolysis of (189) in the presence of CTABr has been investigated. Pseudo-first-order rate constants were not affected by either additive but other changes were noted. The effect of mixed MeCN-water solvents on the same reaction has also been probed. 

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